Olefinic hydrocarbons are employed as starting materials in the hydroformylation, or oxo, process, for the eventual manufacture of numerous valuable products, e.g., alcohols, esters and ethers derived therefrom, aldehydes, and acids. Additionally, olefinic hydrocarbons are employed as reactants in the alkylation of aromatic hydrocarbons, specifically for the manufacture of linear alkyl aromatics and linear alkylaryl sulfonates, for eventual formulation into surfactants used in a wide variety of applications. In many of these end uses, linear or lightly branched hydrocarbon chains have advantages compared with more heavily branched chains. In the oxo process, olefins with linear or lightly branched structures are more reactive than those with heavily branched chains and, for a given degree of branching, certain isomers are more reactive than others. In surfactants produced from alkylation of olefinic hydrocarbons and sulfonation of the alkyl aromatic product, highly branched materials exhibit very poor biodegradability. However, linear alkylaryl sulfonates often are not highly effective as cleaning agents. Use of surfactants produced from lightly branched olefin oligomers in detergent formulations is advantageous because such surfactants exhibit acceptable cleaning properties and yet are relatively biodegradable.
Processes for oligomerizing olefins to produce a hydrocarbon material with a reduced degree of branching are well known in the art, for example as described in U.S. Pat. Nos. 4,855,527; 4,870,038; 5,026,933; 5,284,989; 6,013,851; and 6,300,536.
U.S. Pat. No. 4,855,527 describes a process for producing high molecular weight essentially linear hydrocarbon oligomers from a lower olefin feedstock by employing a shape selective crystalline silicate catalyst (ZSM-23) which is surface deactivated.
U.S. Pat. No. 4,870,038 discloses a process for producing substantially linear hydrocarbons by oligomerizing propylene or butene by employing a surface inactivated, but internally active, ZSM-23 metallosilicate zeolite catalyst.
U.S. Pat. No. 5,026,933 teaches a process for producing substantially linear hydrocarbons by oligomerizing a C2-C8 olefin with siliceous acidic ZSM-23 zeolite having Brönsted acid activity; wherein the zeolite has acidic pore activity and wherein the zeolite surface is rendered substantially inactive for acidic reactions.
U.S. Pat. No. 5,284,989 is directed to a process for producing substantially linear hydrocarbons by oligomerizing a lower olefin with acidic aluminosilicate ZSM-23 zeolite having Brönsted acid activity; wherein the zeolite has acidic pore activity and wherein the zeolite surface is surface-deactivated for acidic reactions by contacting with oxalic acid.
U.S. Pat. No. 5,874,661 teaches that contacting a branched olefinic hydrocarbon material with a catalyst in the form of a molecular sieve having a 10-membered ring pore structure reduces the degree of branching of the material.
U.S. Pat. Nos. 6,013,851 and 6,300,536 provide a process for the oligomerization of an olefin feed with a molecular sieve catalyst, in which a zeolite surface layer is deposited on each particle of the molecular sieve, the zeolite containing silicon and at least one other selected element, the zeolite of the surface layer being of the same crystalline structure as the core and having a higher silicon:selected element ratio than that of the core. The resulting product is an olefin oligomer hydrocarbon material having a reduced degree of branching.
Hydration of an olefin feedstock in a conventional oligomerization process has been recognized in the art. U.S. Pat. No. 5,672,800 discloses that by using a hydrated alkene-containing feedstock in an alkene oligomerization process, the yields of higher molecular weight alkenes can be increased, and the catalyst becomes deactivated more slowly. U.S. Pat. No. 6,013,851, discussed previously, also describes hydration of an oligomerization feed.
It would be desirable to prolong the life of the catalyst and to control the degree of branching in an oligomerization process to produce a substantially linear olefin hydrocarbon product useful in a wide variety of end use applications.